36 THE NATURE OF ANIMAL LIGHT 



"Wiedemann and Schmidt (1895) as a light accompanying 

 the solution of colored (from exposure to cathode rays) 

 crystals of Li, Na, or K chlorides, is probably due to a 

 triboluminescence from stirring of. the crystals dur- 

 ing solution. 



Chemiluminescence. — As the name implies, chemilu- 

 minescence is the production of light during a chemical 

 reaction at low temperatures. This does not mean that 

 the other types of luminescence are not connected with 

 chemical reactions — using the word reaction in a broad 

 sense — for we have reason to believe that in some cases 

 spectra are not characteristic of the element as such but 

 are rather characteristic of a particular reaction in which 

 the element takes part (dissociation into ions, changes 

 from monovalent to bivalent condition, etc. ) and that this 

 is the reason one element may show various spectra under 

 different conditions (Bancroft, 1913). The chemilumines- 

 cences are rather oxidation reactions involving the ab- 

 sorption of gaseous or dissolved oxygen and may be very ^ 

 easily distinguished from all the previously mentioned 

 luminescences by this criterion. They should, perhaps, 

 more properly be called oxyluminescences. 



The glow of phosphorus is the best known case, recog- 

 nized since phosphorus was first prepared by Brandt in 

 1669. It is interesting to note that when first prepared 

 phosphorus was regarded as a peculiarly persistent type 

 of phosphor, i.e., a material akin to the impure alkaline 

 earth sulphides. 



Fresh cut surfaces of Na and K metal will glow in the 

 dark for some time, especially if warmed to 60°-70° 

 (Linnemann, 1858). A film of oxide is formed over the 

 surface, showing definitely that oxidation has occurred. 



